Sextant marking device



Dec. 14, 1948. l. w. DOYLE 2,456,392

SEXTANT MARKING DEVICE Filed Jan. 31, 1945 5 Sheets-Shoat 1 INVENTOR vhaw/v6 (0on5- EYS Dec. 14, 1948. w, DOYLE 1 2,456,392

SEXTMIT MARKING DEVICE Filed Jan.' 31. 1945 5 Sheets-Shoot 2 ALTITUDE.TIME

mvzmoa lnvm'a W Davis F 1948- l. w. DOYLE snmm'r hummus DEVICE 5Sheets-Sheet 3 Filed Jan. 31. 1945 INVENTOR flew/v0 W Dov/.5

ffkZ J TTOR EYS ii NE Dec. 14, 1948. 1. w. DOYLE 4 2,456,392

SEXTANT IARKING DEVIUE Filed Jan. 31, 1945 5 Sheets-Sheet 4 .FJ ]UlNVENTOR J /RV/NG W DOYLE BY ah,

ATTOR EYS Patented Dec. 14, 19 48 SEXTANT MARKING DEVICE Irving W.Doyle, Massapequa, N. Y., assignor to Fair-child Camera and InstrumentCorporation, Jamaica, N. Y., a corporation of Delaware ApplicationJanuary 31, 1945, Serial No. 575,499

This invention relates generally to sextants, and more particularly toan automatic marker for a sextant for averaging a substantial number ofinstantaneous sights to obtain an accurate reading or fix.

Due to the fact that the natural horizon is very dimcult to see from anaircraft in flight, except at altitudes below 1,000 feet, an artificialhorizon must be employed in an aircraft sextant. A spirit level, apendulum or a vertical gyroscope might conceivably be used for thispurpose. Gyros tend to accumulate errors over significant periods oftime, and pendulums usually have excessive friction in their bearings,so most aircraft sextants employ spherical bubble levels to indicate thehorizon.

Due to the effect of the accelerations of the aircraft upon the fluid inthe bubble chamber, this form of artificial horizon is subject toinstantaneous errors of large magnitudes. These errors, however, changetheir sign quite regularly, and if the average indication is takenreasonable accuracies can be obtained.

From studies made of the pitch, yaw and change of speed characteristicsof many different types of aircraft, it has been found, particularlywith respect to yaw, that the spirit level bubble reacts differently fordifferent size aircraft. For a large aircraft, the oscillationsresulting from yaw are of the order of 1.5 cycles per minute, whereasthey are 3 to 4 cycles per minute in smaller aircraft. Theseoscillations of the aircraft probably result from the pilot'sovercontrolling in one direction or the other as he endeavors tomaintain his aircraft on its true compass course. Thus as he turns tostarboard, for example, to return to his compass course, there is areaction in the bubble chamber of the spirit level, i. e. by reason ofthe inertia of the liquid in the spirit level the bubble partakes of acharacteristic oscillation which more or less follows the oscillation ofthe aircraft. Accordingly it follows that when the bubble is at thelimits of its cycle of oscillation, the acceleration is greatest andaccordingly the error is greatest. Hence to achieve an acceptableaverage observation, the individual sights must be made during allphases of at least one full cycle of the plane's oscillation. Thereforea certain minimum time must pass during the sighting P riod, and sightsmust be recorded at reasonably uniform intervals of time. A sightingperiod of from one to two minutes has been found to produce the bestresults. Longer periods produce errors attributable to fatigue of theoperator.

Claims. (Cl. 346-2) when a navigator undertakes to perform thisoperation manually, he inust hold constant collimation with thecelestial body. and at equal intervals of time, record the sextantreadings. This is done on a sextant of the type described hereinbelow byrotating with one hand the knob which moves the prisms while sights arerecorded by manually pushing with the other hand a button which makes arecord on a disc. The disc is geared to the prism mechanism so that theposition of each mark indicates the prism position for each observation.By simple judgment or by counting to find the middle mark on the disc,either a weighted average or median average can be obtained.

Investigation of actual practice in the field shows that navigatorscannot always maintain collimation to their satisfaction, and for thisreason fail to record their sights at uniform intervals. This oftenresults-in more sights being taken when the bubble error is at a maximumthan at a minimum. Further, some navigators record their sights onlywhen relative motion between the bubble and the body is least. Thistechnique results in large errors because the least relative motionoccurs at the time when the bubble is most inaccurate; at the time whenthe acceleration is at maximum and the bubble is about to reverse itsdirection.

In order to avoid these natural psychological traits, it is necessary totake the determination of the instant of marking out of the control ofthe navigator and cause them to be automatically made at equal intervalsof time. This leaves room for complete concentrationon the part of thenavigator upon continuous collimation. Thus the navigator may be taughtto collimate anywhere in the field of view rather than only in thecenter. This technique is Justified when it is realized that thedeflection of the bubble is mainly caused by. the acceleration of theplane and not by tilt of the aircraft or sextant. To

correct, by tilting the sextant, a displacement of the bubble which iscaused by acceleration, is to introduce still further error.

While diiferent types of so-called averaging devices have been proposed,and indeed used to a certain extent, their averaging function wasincapable of overcoming these difllculties. Certain types of sextantsemployed automatic averaging and marking mechanism which had a fixedtime interval of operation, the arrangement being such as to necessitatethe taking of successive readings throughout the entire period in orderto obtain an average. When it is realized instill l 'l that in manyinstances readings cannot be taken for more than thirty seconds, for because of the celestial bodys becoming cured, or of the necessity ofevasive action, it will he appreciated that if the averaging device hurla total period of operation in excess of thirty sec-- onds. an averagecould not be obtained. Still other mechanism of this character lull totake into consideration the human tendencies and proclivities theobserver, and according y could obtain indifferent averaging underconditions of normal use.

It is accordingly among the objects of l y vention to provide anauton'latic average .mech anism for a sextant of the at" icial. which is(El able oi obviatlr the to ill difficulties 1. addition to ct ore. It aher object to provide mechanism c this nutui which can be directlyattached to t soil it v vhout materially increasing the wl'light withoutdisturbing the normal. opemt Another object is to orovidc much abovenature which simp construction, and yet sufll conditions of extended orther object .10 provide In actor whiclil, by reason of L, of operation,does not for normal of the sextant. in part apparent and in partlDOilZllt inafter.

tures of construction, comb "lotions oi and arrangements of parts asvill be in the structure to be hereinafter dccol-il the scope of theapplication of which wi dicated in the following claims.

In the drawing wherein. I have shown villi forms of my invention,

Figure 1 is a perspective View of the artificial horizon type to whichti preferred form of my automatic averaging and marking mechanism isattached;

Figure 2 is an enlarged elevation, partly in section, of the markingportion of the nicchanism;

Figure 3 is a sectional elevation taken along the line 3-3 of Figure 2;

Figure 4 is an enlarged plan view of the elec trically operated timingdevice employed in the mechanism, the cover being removed;

Figure 5 is a side elevation of the recording disc having marks thereonillustrative of a typical pattern or grouping resulting from the takingof a number of sights over a period of time;

Figure 6 is a plot of altitude against time illustrative of thevariation in readings taken over a period of time;

Figure 7 is an elevation, partly in section, showing a. modified form ofthe automatic averaging mechanism;

Figure 8 is a. side view of the sextant shown in Figure 7, a portionthereof being broken away;

Figure 9 is an enlarged side elevation (with cover removed) of stillanother form of the marking device adapted to be attached to the sextant(not shown) certain portions being broken away, and others being shownin section Figure 10 is a sectional view taken along the line lO-IU ofFigure 9, a portion thereof being broken away; and,

Figure 11 is the wiring diagram for the embodiment shown in Figures 1-4.

Similar reference characters refer to similar rirton type a oi outvarious views cl? tilui draw a It, I have shown a sextant, i, c. a dwith icl horizon. in general this sextant o. body l5 which supports anoptical oi; shown) part of which is eyepiece body 55 which houses theoptical sysliould level it. The sextant is operated is of a knurled knobHi, this hob being to the movable portions of so operates an indicatoriutaucous and averaged readings ducted at and a marking ;e at iich isoperated vice to .no .cccssivc marks on regularly F e intervals.

ore clearly t, the tlmvice colon.

v t a.

for a light, which y ill and a rheostat 28 sity of illumination of whichwill be described. Clock .ncludes upper and lower supportolates and. illwhich are held in spaced lOll by posts huts l. Also secured to posts onpoles l 33 in the general 11 of a. ll, base of 11 extends through coilcement includes a flywheel whose sh ll (not shown) is pivotally mountedc Ween sui 1e hearings carried by supports 29 30, respectively, B.conventional hair spring (not shown) being fastened in the usual mannerthe flywheel. shaft. Flywheel 35 is adapted, upon energization M, tooscillate hack and forth. As it passes through central point of itsoscillation, a pin 3t extending downwardly from the flywheel tlisencagescontact spring 31, which is fastened to a post 38 extending upwardlyfrom bottom support 3i]. When pin 35 touches :ontact spring 31, coil M mmomentarily energlued to produce a magnetism in the poles 32 and 33.Since flywheel 35 cut away in substantially the shape shown in Figure c,this momentarily produced magnetism attracts the protruding portion ofthe flywheel, giving the oscillating mechanism an impulse. The motion ofthe flywheel is such that the pin 35 sweeps by and disengages contactspring 31, opening the circuit as the flywheel poles approach the fixedpoles 32 and 33 in either direction of operation, but before the polesactually reach the center point. The hair spring returns the flywheel tothe point where contacts 38 and 31 reengage, thus completing one cycleand starting the next. This combination of the flywheel and itsassociated parts, i. e. the hair spring (not shown), pin 36 and contactspring 31, provides a movement having a fixed frequency of operationregardless of voltage or temperature variations.

Fastened to the shaft of flywheel 35 is a wormshaped cam 39 which coactswith a toothed wheel 40 in such a manner that the cam indexes the wheelone tooth for each oscillation of the flywheel. Ioothed wheel 40 ismounted on a shaft II, the opposite ends of which are supportedrespectively in bearings 42 and 43, which are fastened to bottom support30 and extend upwardly therefrom. Mounted on shaft 3|, so as to berotated thereby, is a contact drum 44 which is brushed at one end by acontact strip 45. The

other end of the drum carries a star wheel 48 or the like, the points ofwhich intermittently engage a contact strip 41 thereby electricallyconnecting strips 48 and 41 through the drum.

As will be pointed out hereinafter, contact strips 45 and 41 areelectrically connected to relay 21 so that when contact strip 41 engagesone of the points of star wheel 48-, -a circuit, including a'source ofpower, as well as relay 21, is closed, thus energizing the relay.Energization of the relay in turn closes the circuit to marker 23 m(Figure 1) causing a mark to be made on disc 28. It may now be seen thatas long as coil 34 (Figure 4) of the timer is energized, the timer willcreate successive accurately timed impulses for operating the marker.

While timer 22 has been described as, and indeed preferably is, anelectrically energlzable device, my invention should not be sospecifically limited, as under various circumstances the intermittentimpulses or signals transmitted by the timer may be as accurately andeffectively transmitted by the operation of a simple clockwork mechanismderiving its energy from a spring.

Referring now to Figures 2 and 3, marker 28 is housed in a case 48 whichis fastened to the protecting rim 48 (see also Figure l) of disc 28, asby a screw 58 (Figure 2). An inverted L-shaped bracket (Figure 3) hasits shorter leg 52 attached to the back of case 48 by screws 58, a

solenoid coil 54 being attached to the bracket by means of a screw 55. Asolenoid armature, generally indicated at 56, is right angular in shape,including an armature portion 51 and a stylus support 58. Armature 58also includes a pair of lips 58 and 68 (Figure 2) through which extendsa pin 8|, the outer ends of which are carried in the ears 82 and 83 of abracket 64 fastened to bracket 5|, as by screws 85 and 88. A spring 81(Figure 3) is coiled about pin 8|, having one end bearing against thearmature, and its other end 88 extending through a hole in bracket ear82 so as to keep the armature under a constant counterclockwise bias,urging the armature portion 51 away from coil.

The lower end of stylus support 58 has formed at right angles thereto apair of ears 88 and 18, which carry a pin 1|. On the opposite ends ofpin 1| are supported the ears 12 and 18 of a stylus generally indicatedat 14, comprising a lead holder 15 and a tail piece 18 which abuttingagainst stylus support 58 limits clockwise movement of the stylus. Alead 11 is adjustably carried in stylus 14 and may be set at variouspositions by manipulation of a thumb screw 18. A spring 18 coiled aboutpin. 1I biases stylus 14 clockwise, tending to maintain tail piece 18and stylus support 58 in engagement.

When solenoid coil 54 is energized, as occurs every time an impulse iscreated by timer 22 (Figure 4), armature 56 is pivoted clockwise, asviewed in Figure 3, forcing stylus lead 11 against the face of disc 28to make a short radial mark thereon. Upon deenergization of coil 54, atthe end of the impulse, spring 81 returns the armature to the positionshown, withdrawing the stylus from disc 28. It may now be seen thatevery time an impulse is created by the timing mechanism described, amark is made on disc 28. The impulse is of such short duration, however,that the marks, such as marks M (Figure 1) are substantially radial inspite of the fact that the disc may be rotating in one direction or theother, at

portion of casing 48 for operation by the observer.

Engagement of contacts 8| and 82, upon depression of push button 88,closes the circuit to the timer, causing the creation and transmissionof accurately timed successive impulses to the marker, which accordinglymakes a succession -of marks on disc 28 at accurately spaced intervalsof predetermined amount.

To facilitate use of the sextant and its associated averaging marker atnight, a small electric light 84 is carried by the marker housing 48(see Figure 2). The light extends into the casing adjacent a lightconductor and distributor 85. Distributor 85 is formed of a clear,transparent plastic material having the property of light conductivity.Distributor 85 includes a pair of feet 88 and 81, and also an attachingarm 88 by which the light distributor is fastened as by screws 88 to thewall of casing 48. Feet 88 and 81 straddle stylus 14 and extend inwardlyover the edge of disc 28 so that when light bulb 84 is energized, lightrays emanating therefrom are conducted by the. light distributor intothe disc housing, thereby to illuminate the upper portion of the disc.

The light is also conducted by feet 88 and 81 along opposite sides ofstylus 14, and as the illumination on both sides of the stylus issubstantially equal, the stylus does not cast a shadow on disc 28. It isthis bulb 84 which is controlled by switch 28 (Figure 4). A similarlight bulb 88 (Figure 1) is provided in liquid level I8 to illuminatethe bubble, this bulb being under the control of rheostat 28 (Figure 4).

The complete operation of the automatic marking mechanism will bedescribed in connection with Figure 11.

A source of current is provided preferably by a detached dry cellbattery 8|, which may conveniently be a suitable number of flashlightcells contained in a battery case 8Ia. Battery 8| is connected to groundby a line 82. The battery is connected to timer 22 by a cable having apair of leads 88 and 84, the first of which goes to I battery 8|, andthe second of which is grounded.

Cable lead 83 connects with a line in the timer unit which is connectedthrough a series resistance 88 to rheostat 28, the rheostat in turnbeing connected by a line 81 going to one side of the bubble chamberlamp 88, the other side of this lamp being grounded by a lead 88.

A lead 88 connects line 85 with one side of switch 28, the other side ofthis switch being connected by a line I88 with the marker unit lamp 84,this lamp being grounded by a line I8I. A second line I82 connectsstationary contact 8| in marker unit 28 with line 85, while a third lineI83 connects line 85 with clock movement 25. This line I83 is connectedto one end of the clock movement coil 84, the other end of which isconnected by a lead I84 with spring contact 81. Pin 38 which, as notedabove, is carried by flywheel 85 (Figure 4) is in Figure 11illustratively grounded by line I85. Strip or brush 45 of the clockmovement is connected by a line I88 to one side of coil I81 of relay 21,the other side of this coil being connected by lines I88 and I88 to aline H8, in turn connected to movable cnnl incl; 8!, Lille illl is alsoof the stylus solenoid coil l, which, is connected by a lio cry contactH2 of relay tact Hill of relay 2'! is c to a line M5 which grouncs relectric clock movement (use also 1: Il: will now appear that wlL, inccted to the sextant, the established: battery 9!, lead I03, clockmovement coi a l, tacos 31 and 36 and load Hill cordingly back tobattery 31] leads M and 92. As note nation of coil 34 efiects us andaccordingly rotation noted hereinabove, rotctl wheel 48 intermittently cl! to create successive acc for the intermittent l. e, a circuit tomarker 23 l as follows: battery al, lo

i oosrmoble nccui my e disc ill in one l,

c or ...s oth position, and color 2i, it geared to lndlcl ll bake a reorlnzocmbered in it follows that chic cw emged" residing; "led with thepreclusion of errors nth terlng by 1' non of normul psychological tencircles or rcaclzl us of the obcervcr. avcmo rccdlngma be obtained tPvlcc -r various Thus the light be visible but for nd, or two or morc"cl icr cvent, uverl l rough the accuracy have shown anolzhlt ging andmoi-kl cc ill iigure 8), housing ill, knob ill and "lin 45. In thisform, J. :ord ill, as uhown in the sextant of Figure l, is Jloccd by arecord disc ill (.lfilgure "1) which .r. outside of iii, but is,however, o in the inc l3 inner as disc illl. disc ll, lO'lZL accordancewith knob ii}. A disc ill rotates, it has a b.

' atlcally inscribed thereon by c :5, ll nncr now "to be described. As iin Figure 8, stylus i ii) is inountcrl n urm ii iii, the other end ofwhicl'i H and loud i to grounlfi, ow other side oi? the battery. 41 areintermittently c0 is intermittently energize no cause engagement ofcontacts .ll'll am these contacts are engaged, the follow to the markersolenoid coil il l is lead III), which is connected to described above,coil 54, icon, ill, and H3 to ground. Thus i; only marker solenoid coil54 is intcrm gized so that at accurately timed inter i 14 is actuated tomake a murlt, as noted a'oov signed 5 3051; gm pivg'bany t d in th It ynow be Seen that when the ob rver is use lid! of th u'uornatic averagingand markin operating the sextant shown in Figure he :lnuln. device,which is genemny indicated at It is tains push button 83 depressed toeffect cumin-u" noted this point t t t device 12 may be us p ti of themarker as described, and at secured in any suitable manner to thesextant. the same time manipulates knob l9 while looking ilgd about[305; no is a Spring 3 having one t r u h y pi ce 16 n order t bring thebubble end 124 anchored to arm H9, the other and 12s in liquid level I!into coincidence with the hcav- 45 f th pring bging m stationary in anym. 3 y with respect t0 which e 15 taking the able manner. Thus thespring imparts a constant si ht. t th plat m f which the observercounterclockwise bias to arm H9, as Viewed in 15 taking s ts VE 1 if tflbserlel Figure 8, so that when released, the arm, and moves whiletaking the sight, the bubble in the accQming1y Styms 3 is driven in acmmterliquid level will move accordingly and heme clockwise direction toinscribe a time-altitude in i CeSSltflte substantially continuous backand fOlth curve since th movement, f the stylus is a adjustment of knobI9 as the observer endeavors fu ti f time, and the movement of record tomaintain the bubble and the heavenly body in disc H1 is a function ofaltitude, the relative coincidence. Thus over a Of time, the Ohmovements of the tylu and disc accordingly Se ver 15 in effect taking aninfinite number of 5 create a time-altitude curve. In order, however,sights, a plot 01' w ch may t t e app to control the rate ofcounterclockwise movement of t e cu ShOWn 111 Figure It follows that ofarm H9, the arm is connected by a gear train if this curve can bedivided i tO predetermined to a governor I26 which accordingly controlsthe accurate tim te a e p intervals rate of movement of the arm. To thisend, there of one second, it would be possib e o Obtain an is fastenedto post I20, so as to rotate therewith, averaged reading which would bequite accurate. a gear sector z1 which meshes it a pinion In In eflethis is the result Obtained by the autofastened to the same shaft I29 asis a large gear matlc ave i mechanism hel'embefPre I30. This large gear,in turn, meshes with a pin- Scflbedy which there 15 marked on @1150 29 3ion l3! mounted on the same shaft 132 as asecond pattern, such as isshown in Figure 5. From this large gear I33, which meshes with a pinionI pat it may b seen t there is a prepondermounted on a shaft I35. Thisshaft also carries 8110B grouping of marks at A and B in the atiming camI36, as well asalarge gear l3! which upper left-hand and upperright-hand quadrants, through a pinion I38 lsconnected in any suitablewith variously Spaced stray markings therebe' manner such as by suitableshafts and bevel gears tween and Opposite Sides thereof- From this (notshown) to governor I26. Thus gears I21- Krouping the Observer canestimate with reason I38 constitute a gear train between arm H9 and ab yaccu t t position on disc 10 which governor I26, by which the rate ofmovement of resents a. reasonably accurate average. which gives the armis maintained at a substantially constant him the final flx betweengroups A and B. If value.

there is a preponderance of the markings adja- Preferably engagementbetween stylus Ill and disc I" is eifectedintermittently at accuratelytimed intervals. To this end, the stylus is preferably reciprocablymounted in a housing I40 (Figure '7) in which is disposed a smallsolenoid I by which the stylus may be intermittently reciprocated. Thissolenoid is included in the circuit of a pair of contacts I42 and I43(Figure8) which are intermittently engaged, for example, one everysecond, by timing cam I36. The circuit for these contacts also, ofcourse, includes a source of power (not shown) which, as in the case ofthe averaging and marking device described in ,Figures l-4, mayconveniently be dry cell batteries contained in a carrying case. Thus itmay now be seen that when arm H9 is setto its extreme clockwise positionand released it will follow a substantially radial path of movement fromthe rim toward the center of recording disc II 1 at a controlled rate,while at the same time stylus III will intermittently engage the recorddisc through the operation of timing cam I36 and contacts I42 and I43.Thus, at the end of the period of counterclockwise travel of arm I I9,stylus I I8 will have made a series of dots on record disc II1, whichwill take the form of a time-altitude curve the nature of which, ofcourse, depends on the movement of record disc Ill in response to themanipulation of knob I9 by the observer. Thus this curve may in certainrespects resemble that shown in Figure 6. In any event, the curve may beaveraged visually by the observer to give h m an altitude reading of theheavenly body sighted.

In Figures 9 and 10, I have shown the third form of my automaticaveraging and marking device (with cover removed). In this form I havenot shown the device as attached to the sextant, it being understoodthat it is readily so attachable as properly to present its stylus tothe surface of the sextant recording disc. In Figure 9, a timing unit isgenerally indicated at I44, a marking unit being generally indicated atI45, both of these units being fastened to a supporting plate I46 towhich the cover of the device is secured in any suitable manner. Thetiming unit I44 includes a reluctance motor, generally indicated at I41,comprising a. two-pole laminated field magnet I48, and an oscillatablearmature I49, having windings I49a. Armature I49 is secured to a shaftI50 (Figure 10), the lower end of which is rotabaly supported in abearing I5I (Figure 9), the upper end thereof being supported in a topplate I52. A bracket I53 is fastened to the upper end of shaft I50 andhas connected thereto one end of a spring I54, the other end of which isanchored in a depending lug I55 secured to top plate I52. As shown inFigure 10, spring I54 imparts a constant counterclockwise bias toarmature I49, and accordingly opposes clockwise movement of the armatureupon energization of motor I41.

Secured to, so as to move with-armature I49 is an arm I56 extendingoutwardly through a slot I51 in field magnet I48 to engage and operatemarker I45 when motor I41 is energized, as will be described in detailbelow. Fastened to and extending upwardly from arm I56 is a finger I59,the upper end of which carries a contact button I59 (see also Figure10). This contact button is adapted to engage a contact button I60mounted on a lug I6I, secured to and depending from a plate I62. Thisplate is fastened to a hub or sleeve I63, which is freely mounted onshaft I50. Thus plate I62 is rotatable relative to armature 9.. Plate I62 has another lug I64 dependm, and to this lug is fastened one endstarts to rotate plate I 62 counterclockwise. The

of a spring III, the other end of this spring beingment, as well asforcing arm I56 against a post or stop I69.

Referring back to Figure 9, plate I62 carries a pawl I69 adapted toengage and accordingly drive a ratchet I10 during counterclockwisemovement of the plate, as viewed in Figure 10. Ratchet I10 is freelymounted on shaft I50 (Figure 9) and is connected through a gear train(not shown) to a conventional escapement mechanism or governor, asdesired, which not only governs the period of the counterclockwisemovement of plate I62, as viewed in Figure 10, but also maintains itsubstantially constant. The escapement or overnor; may be convenientlyhoused between upper and intermediate plates I52 and I61. Plate I62 alsocarries an arcuate shaped weight "I which increases the inertia of theplate for a purpose which will be disclosed.

As noted hereinbefore, reluctance motor I41, when energized, rotates,arm I56 (Figure 10) clockwise, the arm accordingly driving the markingdevice I45 the limit of its travel. This limit of travel of the markingdevice accordingly constitutes the limit of possible movement of arm I56and accordingly contact button I59 carried thereby. The limit ofmovement of plate I62, however, is determined by a pair of lugs I12 andI13 carried respectively by plate I62 and intermediate supporting plateI61. A certain amount of adjustment is provided by a set screw I14extending through lug I13. These lugs I12 and I13 are so arranged as topermit an over-travel of plate I62 in relation to thetotal extent ofmove- 'ment of arm I56 upon energization of the reluctancemotor.Inasmuch as when the motor is energized, arm I56 reacts strongly andsuddently,

plate I62 (which is driven by finger I58 and lug I 6|, Figure 9) gainssubstantial momentum, by reason of inertia plate "I, which is sufilcientto continue the rotation of the plate throughout the extent ofover-travel of which it is capable, which over-travel effects aseparation of contact buttons I59 and I60. These buttons constitute aswitch in the circuit of motor I41 so that when the contact buttons areseparated,- the circuit to the motor is broken, effecting itsdeenergization and accordingly permitting immediate counterclockwiserotation of arm I56, as viewed in Figure 10, by spring I64.

' When lug I 12 (Figure 9) engages set screw I14 in stop lug I13 theplate spring I65 (Figure 10) rate of movement of the plate, however, iscontrolled by the escapement or governor hereinabove referred to so thata definite period of time elapses before the plate-rotates sufllcientlyto effect reengagement of contact buttons I59 and I60. When, however,these buttons reengage at the end of an interval of one second, forexample, motor I41 is reenergized and the cycle is recommenced. Thus foreach excitation of themotor, marking device I45 is driven so that itsstylus, described below, makes a mark on record disc 20 (Figure l) ofthe sextant.

Marker I45 conveniently includes upper and lower plates I15 and I16pivotally connected by a rear link In and a pair of front links In andI19, the rear link I11 :being slotted as at I00 for the admission or armI56 between upper and cases 11 lower plates I" and Hi to engage a lipIII depending from the former. upper plate I15 (Figure 10) is secured adepending bracket I" which carries a post I"; this post carries at itsouter end a stylus or lead I. Bracket I82 also has secured thereto oneend of a spring I", the other end oi which is anchored to a post Isecured to bottom plate I16 (Figure 9) this spring acting to return thestylus. and also to assist in returning arm iii to their Figure 10, orstarting, positions, upon deenerglzation o! the timer motor. It may nowbe seen that when the circuit or timer motor I" is closed, as by asuitable manually operable on-oil switch '(not shown), the motor isintermittently energized through the making and breaking of contactbuttons III and I", as described in the preceding paragraph. Thisintermittent ener'gization or the motor accordingly intermittentlyreciprocates stylus I of marker unit I at accurately nxed intervals, soas to mark the record disc 20 (Figure l) oi the sextant,'in the mannerdescribed in connection with marker 23. While I have not shown thecircuit oi timer motor I", it will be understood that this is a simpleconventional circuit including the timer motor, contacts I SI and I", asource of power and a conventional manually operable switch. Thus itfollows that as long as such switch is closed, the timer motor iscontinuously intermittently energized so that marks are made on therecord disc automatically, permitting the navigator to focus his entireattention on collimation.

Accordingly I have provided an averaging marker for a sextant, whichattains the several objects set forth hereinabove in a thoroughlypractical and emcient manner.

As many possible embodiments may be made of the above invention, and asmany changes might be made in the embodiment above set forth. it is tobe understood that all matter hereinbefore set forth or shown in theaccompanying drawing is to be interpreted as illustrative and not in alimiting sense other than required by the definition of the appendedclaims.

I claim:

1. In apparatus for recording successive sights taken with a sextant,said apparatus comprising, the combination of, means for movablymounting a re o din m ans adapted to be mounted on said sextant adjacentsaid movable member for making a mark thereon, an element forintermittently operating said marking means, a solenoid for driving saidelement, a circuit including a source of power for said solenoid, saidcircuit also including a pair of disengageable contacts, means mountingone of said contacts on said element, a movable part adjacent saidsolenoid, said other contact being mounted on said part whereby saidpart is driven when said solenoid is energized, means for limiting thetravel of said element relative to that of said part whereby said partis capable of a total movement in excess of that of said lastmentionedelement thereby to disengage said contacts and break said circuit, meansfor returning said solenoid to its starting position, and means forreturning said element to its starting position but at a slower rate,whereby said solenoid is intermittently energized.

2. Apparatus according to claim 1 wherein said returning means includesan escapement mechanism.

3. A sextant comprising, in combination, a body and associated housing,means for mounting a record member in said housing ior movement in Tothe front end of 12 one direction or another in accordance with thedirection of adjustment of the sextant, a casing mounted on said housingadjacent said record member, a stylus mounted in said casing for makingmarks on said record member, illuminating means mounted in said casing,and light conducting and distributing means operatively associated withsaid illuminating means in said casing for conducting light therefrom tosaid record element on opposite sides or said stylus.

In apparatus of the character described, in combination, a navigatinginstrument, manually operable means for adjusting said instrument,recording means including a stylus on said instrument operable forrecording successive instantaneous readings as the navigator adjusts theinstrument, a solenoid including an armature mounted on said instrument,means connecting said stylus to said armature, and means including aswitch operable by the navigator, to effect continuous intermittentenergization of said solenoid and thereby intermittent recordingoperation of said'stylus at regularly timed intervals exclusive oi thenavigators control as long as the navigator keeps said switch closed tomaintin energization of said solenoid.

5. Apparatus according to claim 3 wherein the light onducting anddistributing means includes a pair of members so mounted adjacent saidhousing as to straddle said stylus.

6. Apparatus according to claim 3 wherein the light conducting anddistributing means includes a pair of members so mounted adjacent saidhousing as to straddle said stylus, said light distributing meanscomprising a. unitary member secured to the sextant body.

'7. Apparatus according to claim 4 wherein the solenoid, armature andstylus are disposed in a housing, and means for attaching said housingto said sextant, whereby the solenoid, armature and stylus comprise aunitary assembly applicable as such to a standard sextant.

8. In apparatus or the character described, in combination, a sextant,manually operable means for adjusting said sextant, recording meansincluding a marking device on said sextant operable for recordingsuccessive instantaneous readings as the navigator adjusts the sextant,energizable means connected to said recording means and operable duringenergization to eflect continuous operation of said marking device, andswitch means in the circuit oi. said energizable means for manualoperation by the navigator to effect energization of said energizablemeans, whereby as long as the navigator holds said switch means closedsaid recording means operates continuously.

9. Apparatus according to claim 8, wherein said circuit includes switchmeans, and a source of power, said circuit also including a secondswitch adapted to be intermittently opened and closed, said circuit'being energized when both of said switches are closed, and meansoperatively associated with said second switch for intermittentlyopening and closing it.

10. Apparatus according to claim 9, wherein the means whichintermittently closes said second switch includes a clock movement,whereby said second switch is closed at regularly timed inter vals.

IRVING W. DOYLE.

(References on following page) 3 nnmmcns crmn Number 14 Name DateLepetlt Mar. 31, 1942 Page Apr. 28, 1942 Hobbs Feb. 1, 1944 Inwkrantz eta1 y 1 4 FOREIGN PATENTS Country Date Great Britain May 9, 1922 FranceDec. 28, 1936 France Dec. 7, 1939

